latte glass cake

Hi all Decorators

Help needed, I have been asked to make a latte cake in the form of a tall glass that is thinner at the bottom. Originally chocolate biscuit which would have been fine. However it has been changed to sponge and I have never done a cake that thin that has to have a thinner bottom and wider top and have some height. Any help would be appreciated, should it be ok if I cake card on way up and dowel all the way through. Thanks all.